The present invention relates to a circuit board improved in heat dissipation and to a method of manufacturing the board.
According to a recent trend of electronic equipment having a higher performance and a smaller size, semiconductors are strongly demanded to have higher density and performance. A circuit board for mounting such semiconductors is accordingly desired to have a smaller size and a higher density. This arises a problem of heat dissipation of, for example, power semiconductors mounted at a high density.
A prior art for improving the heat dissipation is implemented by a lead frame including a conductor, such as a heat sink plate, integrated via a sheet. The lead frame has a circuit pattern formed by punching out unnecessary portions for a circuit from a plate. Upon being punched in a direction to the heat sink plate, the plate has burrs generated due to the punching. The burrs approach the heat sink plate through the sheet, and may cause short-circuiting to the heat sunk plate.
Another conventional lead frame has a circuit pattern including a land for mounting an electronic component. In order to form a land, a plated layer is formed on the entire surface of the circuit pattern, and a resist film is then disposed on the plated layer. The resist film is not formed on a portion of the land, where the plated layer exposes, and the portion serve as a land.
The plated layer on the portion melts due to heat from solder during the mounting of the electronic component, and may move between the lead frame surface and the resist film.
As the plated layer moves, a plated layer on the land become thinner, and this causes defective mounting of the electronic component.
A circuit board includes a sheet, a lead frame which has a circuit pattern and is bonded to the sheet, and a heat sink plate bonded to a surface of the sheet opposite to the lead frame. The circuit pattern of the lead frame is formed by punching a plate from a surface of the plate bonded to the sheet. The circuit board prevents the lead frame from short-circuiting to a conductor, such as the heat sink plate.